Fire control



C. H. SHAW FIRE CONTROL Jan. 1, 1952 Filed March 29, 1946 INVENTOR cHARLEs H. SHAW BY M ATTORNEY Patented Jan. 1, 1952 2,581,149 FIRE: CONTROL Charles H. Shaw, Silver Spring, Md., assignor to the' United States oi.l America as represented by the Secretaryv of the Navy Application March 29, 1946, Serial No. 658,161 1 ciaim. (o1. 604-53) The present invention relates to ditheringarrangements, and, while it has a considerable range of`prospective-application, it is ofparticular utility in improvingfthe operation of remote control systems such as those used in iire control forpositioning a gun.

Remote control systems employed' in fire con-- trol are generally of the continuous-control closed-cycle typeV and have the following principal components: (A) the controlling member, such as a gun director for determining the position to which the controlled member should be ordered; (YB) the controlledV member or gun; (C) a measuring instrument for producing a basicY electrical error signal having a magnitude proportional. to any deviation or departure of the actual position of the controlled member from the position ordered by the controlling member and a polarity indicative of the direction of they departure; -(D) signal amplifying and shaping networks for amplifying the basic .signal and/or modifying it in accordance with one or more functions of the deviation or departure, thereby to determine the characteristics of the controlaction desired; (E) an arrangementcontrolled by the resultant modified and/or amplified error signal for moving the `controlled member in such manner as to eliminate the deviation or departure, thereby to bring the position of thecon'- trolled member into correspondence or synchro'- nism with the position ordered by the controllingv member.

Component (E) generally comprises an auxiiliary source of power for moving the controlled member and regulating means responsive to the above-mentioned resultant signal for determining the rate and direction of application of power from that source to the controlled member. Units (D) and (E) together constitute a followf up or Servo mechanism. Such a mechanism is essentially a power amplifying device in which the amplier element or elements which drive the output are so actuated by the difference between inputv and output' that the output elementv is driven in such a direction as to make that difference approach zero.

The immediate function of the amplified error signal, generally applied Vto a control winding of a reversible electrical stroke control motor, is to control the speed and direction of rotation of the motor rotor In turn, `the immediate functiony of the stroke motor is to control the 'linear motion orapilot valve;

The motion ofthe pilot valve is hydraulically amplified byI al booster piston. The latter has a null or neutral position and is so coupled to some conventional prime-moving arrangement (mechanically geared to the. gun. mount) as to cause the speed of the prime mover (and accordingly of' the mount) to vary in accordance with the displacement of the booster piston from neutral and.

the direction of movement of the prime mover tov vary in accordance with the direction of that displacement. Thus itv will be seen that' the am'- oliled error" signal determines. the setting of' a regulator and the latterv determines the speed and direction ofthe error-correcting action.

AFor ythe purpose of superimposing a vibratory motion upon the motion of the pilot valve (which is governed by the resultant electricalr signal hereinabove referred' to) there-is provided in accordance with the prior-arta dither methanism. This mechanism conventionally consists of a dither motor', a crank andl arm, so arranged with respect to the mechanical linkage between the stroke control motor and the pilot valve as to impart to the latter the desired' vibratory motion; Since the dither action is translated through the' pilotvalve, ythe booster; and the prime mover, Vto the gun mount; the entire hydra ulicand mechanicalY system becomesmore sensitive to movement of the stroke control system. The dither motor facilitates themaintenance of oil between moving parts of the various units of the remote control system, thus keeping them from settling and making metal-to-metal contact and reducing the undesirable effects of static friction. The dither action also decreases the error which would otherwise be allowed in synchronization by nullifying accumulative play between moving parts. This is accomplished by vkeeping the mount end of the series of moving parts at the mean of this possible error;

It is desirable to eliminate the dither motor and thecomplicated crank and armarrangement which mechanically couple it to the pilot valve. Since the primary motionof the pilot valve in the exercise of its regulating function is dictated by the resultant signal hereinabove referred to, the: invention is premised on the theory that the above mentioned' resultant electrical signal may be modulated or modiiied in such manner as also to dictate the secondary or vibratory motion of the pilot valve and' in this manner to avoid the necessity lfor the complicated dither motor mechanism.

limitations of prior-art dithering arrangements by applying to the input of anexisting control imber a vibratory electric signal which is reated in mechanical form at the output of that amber, instead of supplying to the output of e control member a mechanical vibration sigl produced by additional mechanical arrangeents.

It is also an object of the invention to provide l improved dithering arrangement', involving a w simple components, economical in construcan and reliable in operation.

For a better understanding of the present invntion, together with other and further objects lereof, reference is made to the following speci- :ation and the claim appended thereto, taken conjunction with the accompanying drawing,

, which:

The view is a block diagram of a complete connuous control gun mount power drive system, lcluding a preferred form of dithering arrange- ;ent in accordance with the present invention.

The controlling member is a director I I, of any litable conventional type, positioned in train, r example, by its crew, for establishing a line t sight on a selected moving or stationary taret. The director is equipped with any suitable vgnal system for generating electrical order sigals for the purpose of controlling the gun posi- Lon in train. It is customary to employ an elecrical generator of the selsyn or synchro type not shown) for transmitting the' order signal. he generator stator is fixed andthe rotor is eared to the director in such a manner that there transmitted to the power drive an electrical irder signal for training the gun.

Also illustrated are the controlled gun and count I2', likewise conventional in character, and lesigned to respond or to be turned in train to in actual position corresponding to the ordered losition, to the end that a projectile fired from he gun will strike the target.`

The power drive is of the closed-cycle type and ,t includes an error measuring instrument I3, electrically coupled to the director and mechan- .cally geared to the mount by a suitable gear :rain indicated by the dashed line I4, for comparing electrical order and mechanical response,

thereby to produce a basic electrical error signal :rroportional to and in response to a deviation or departure between the ordered position angle and the actual position angle of the gun in train, the polarity of the error signal indicating whether the correcting operation for effecting correspondence between mount and director involves clockwise or counterclockwise motion.

The error measuring instrument generally comprises a control transformer of the selsyn or synchro class (not shown) having its stator windings electrically coupled to the corresponding windings of the generator, and having its rotor mechanically geared to the gun mount I2 through the gears I4. The operation of the error measuring instrument, usually referred to as the B-end synchro, is such that its rotor produces the above mentioned basic electrical error signal when the position Vof the mount departs from correspondence with the ordered position. As the correcting process progresses the gun mount moves the transformer rotor toward such a position that it is not cut by the magnetic iield produced by the interaction of the generator and transformer, so that the error signal approaches zero and attains that limit when correspondence is effected. i

All of the components illustrated in the drawing are conventional in character, with the eX- ception of those included within the double dashed line and indicated generally by the numeral I0. Neglecting for the moment the construction and operation of unit III, it will be assumed that the basic error signal is applied from measuring unit I3 directly to the input of a conventional amplifier and signal shaping network I1 coupled thereto. Uniti'I1 derives from the basic error signal a synchronizing signal having a magnitude related to error and one or more functions of error, according to the control action desired, and a polarity determined by the direction of the angular deviation between gun mount and director. There is coupled to the output of unit I1 a prior-artreversible electrical motor I8 of the drag cup induction type having one of its eld windings connected to unit I1 and the other of its field windings connected through a phasesplitting'capacitor to a reference voltage supply 25. The reference voltage supply is also coupled to the electrical generator in director II, the transformer in measuring instrument I3, and amplifying unit I1, to the end that all of the various signals may be referred to the same voltage and made phase-signicant so that the direction of rotation of the rotor of motor I8 may be determined by the direction of the deviation between gun and mount. Motor I8 is on a common shaft with a prior-art stroke generator I9 and drives the latter, causing it to produce an output damping signal which is fed back to the amplifying unit I1 through any suitable coupling network. The purpose of the damping signal is to stabilize the operation of stroke motor I8 and to prevent oscillations of the gun mount of such frequency as to delay or impair the accuracy of the response of the mount to orders from the director.

'Stroke motor I8. converts the composite signal applied thereto from unit I1 into linear motion of a pilot valve 20. The latter is a prior-art device hydraulically coupled to and operatively determining the ow of oil to one side or the other of a conventional booster piston 2| (the booster piston functioning as a hydraulic amplifier to amplify the linear motion of the pilot valve) The ultimate source of power for moving the mount comprises a constant-speed, high-power electrical motor 22, preferably of the three-phase, induction type. This motor is geared to an A-end fluid pump 23, included in the hydraulic system, and drives the pump in one direction at a constant speed. Pump 23 is hydraulically coupled by two pipe lines and the oil contained or iiowing therein (not shown) to a B-end fluid motor 24, which in turn is geared to mount I2 by any suitable arrangement of gears indicated by the dashed line 26. Motor 24 is of the variable feed hydraulic type, such as the Vickers Model MF-38-2-S98, having an output speed and direction determined by the volume and direction of flow of oil delivered by pump 23. The pump is of the variable delivery hydraulic type, such as the Vickers Model TV-2003, so arranged as to supply oil to the motor at a rate determined Aby the diierence between the angle between tilting and xed members of the motor and the angle between tilting and fixed members of the pump. Each of units 23 and 24 comprises a fixed member and a tilting member (not shown). The angle between the motor. members is fixed, but the pump tilting member is so mechanically linked to the booster piston 2| that the angle between the pump members is varied by movement of the booster piston. When the two angles are, the same,` as when the booster piston is on neutrah the? fluidf pump' does' not deliver any oil tothevfmot'or andthe: mount'is stationary. When the angle betweern the: pump members is' larger' than; that: between the-motor` members, aswhen the pilotzvalve4 is inI an out positionthemotor 24zmovesithefmountin onedirection; .When this angler is smaller than; that between themotor members, as when the pilot valve is oppositely'displaced fronn neutraland in an in position, the mount is moved in the opposite direction.

Units 20, 2li, 2725,23, and'2`4 are'li'ndividually and im their relationship/to eachother ofthe priorart and are hereinafter collectively treated as the controlled power source, since, they function in the aggregate to eliminate the departure betweerrfgun and director by. moving theiormer. toward correspondence. `AThe. controlled'Y power scurceissoiarranged. that. wheirthe stroke motor is: moving with. constant. velocity.'A and the -i' pilot valve is'l being displaced. from". neutral with'V con'- stant velocity, the gun` isbeing'trained with' con;- stant acceleration.. Wih'enf the'A stroke motoris accelerating, the angular acceleration of the gun is increasing. When the stroke motor is stationary, and the pilot valve and booster piston are on neutral, the gun is in static correspondence with a stationary gun order from the director. When the stroke motor is stationary and the pilot valve on neutral but the booster piston is stationary and displaced from neutral, the gun is moving with constant velocity in dynamic synchronism with an order from the director. The

expression stationary is not to be construed topreclude slight vibration due to the dither action.

The controlled power source is regulated by the movement of pilot valve 20. The latter performs its regulating function by causing the stroke of fluid pump 23 to be controlled. Therefore it is customary to refer to the signal transemotelcontrolsystem; In ordertb eliminate stat= i'c friction', to; prevent this'accu'mulative play, and?. tm balancea yone suchiiund'esired factorI- on against another, to the end that gun and mount i2will assume the meanl position, the'novel and improved dither arrangement'. I il to which the description now returns, is provided in' accordance, Withii the `present-fmventionfn 'lnste'adot superimposing*uponv theA mechanical motion of the vpilotv valve (i. e; the output of strokemotor Id) a'. mechanical vibratoryA signal, which'expedient required ktheaprovision folf a -dither motor and complicated m'echanical'linkages, the .inventionr is' addressed to' the application of electrical principles. in superimposing upon the outputm-otion of stroke-motor" I 8; a vibratory motion.

, To this end, a resisten 5" isincluded in vcircuit mittel' included in director II as the signaling system, to units I3, I 4, and I'! to 2D, inclusive, (and their associated circuits) as the stroke control system, to units 22, 23, and 24 as the hydraulic system or auxiliary source of power, and to booster piston 2| as the connecting link between the stroke control system and the hydraulic system.

The operation of the illustrated system is such that a deviation or departure of the gun mount from correspondence with the director order signal is detected by error measuring instrument I 3, which then generates a basic electrical signal indicative of the magnitude and direction of the error. This signal is electrically amplified in amplier I1 and converted into rotary mechanical motion by stroke motor i8, which motion is in turn converted into the linear motion of pilot valve 20. When the voltage applied to the control winding of motor I8 is substantially 90 behind the reference voltage applied to the reference winding, the motor rotates in one direction. But when the control winding voltage is substantially 90 ahead of the reference winding voltage, the motor rotates in the opposite direction. The linear motion of the pilot valve is hydraulicaly amplined by booster piston 2l and utilized to regulate the behavior of the auxiliary power source. The result is that as soon as error apears in the system an appropriate correcting process is initiated and correspondence is restored. It will be seen that the system contains numerous mechanical components and gears. Their static friction and backlash or play impair the accuracy and rapidity of action of the betweenerror measuringinstrument I3 and` arnpii-ierlr'icfzhise .resistor is:v coupled. to Ythe: tank circuit of. a conventional; electronicfvacuum. tubeoscillator It, having an output signalV frequency of,L say, cycles. per second,4 related to thefreqnenoyf vibration; desiredi'andf am output; signal; amplitude small in comparison to the magnitude of the basic carrier signal from instrument I3 which dictates the primary movement of motor I8. Oscillator IS modulates at its frequency the basic carrier signal from unit I3, and both the oscillator output signal and the basic signal are combined in amplifier I'I. Source 25 preferably has a frequency of the order of 60 cycles per second, so that the signal from the oscillator alternately leads and lags the reference signal applied to that phase of motor I8 which is coupled through the phase-splitting capacitor to source 25. Although the general vdirection of rotation of motor 58 is determined by the synchronizing signal component of amplifier I 1, the output signal from oscillator Itk cyclically urges motor I8 in one direction and then in the other. When the gun mount is in correspondence with the director, the only signal component translated from unit I1 to the control winding vof motor i3 is the amplified oscillator signal, so that the motor and pilot valve then have a slight vib-ratory motion. This slight vibratory motion as transmitted to the gun mount I2 through units I8, 2li, 2I, 23, 24 and 25 causes the mount to remain in the mean position of synchronism.

Likewise, when mount I2 is in dynamic synchronism with director II and moving at constant velocity with the director, the booster piston is vibrating about a position displaced from neutral, since no signal is then applied by amplifier I1 to motor I8, other than the amplified output signal of oscillator I 6.

While there has been shown and described what is at present considered to be a preferred embodiment of the invention, it will be obvious to those skilled in the art that various modications and changes may be made therein Without departing from thev true spirit of the invention, and it is, accordingly, intended in the appended claim, to cover all suchl changes and modications as fall within the true scope of the invention and without the scope of the prior art.

lWhat is claimed is:

Control apparatus for positioning a gun mount in accordance with electrical gun orders transmitted from a director including a stroke motor including a rotor and a stator, said stator having a control winding and a reference voltage winding energlzable'by a reference voltage of predetermined frequency, a hydraulic system comprising a, fluid motor for driving said mount,

electrically driven pump for supplying fluid said fluid motor, a boosterpiston mechanically mected to said pump for controlling the fluid ivered therefrom in accordance with the ear position of said piston, a pilot valve hyiulically coupled to and operatively controlg the now of fluid to said piston for positiong said piston in accordance with the linear posin of said valve, means mechanically coupling .d `rotor to said valve for moving said` valve .early uponV rotation of said stroke motor, an ;trum,ent for generating an error signal of said edetermned frequency and of aimagnitude. fiable in accordance with the departure of e actual position of said mount from the posiln ordered by said director, and of a polarity iicative of the direction of departure, an am- `fier for said-error signal, *a stroke generator nnected to said rotor, means for degeneratively :ding the output of said stroke generator to id amplifier, means connecting said amplifier circuit with said control winding to rotate said tor in one or the other direction as determined by the phasefrelation -betweensaid amplifier error signal and said reference voltage, 'means for dithering the linear movement of the pilot valve comprising a thermionic oscillator-having a Voltage output of a frequency differing from said predetermined vfrequency and means for superimposing upon said error signal in circuit With` said amplifier the output volt-age of said oscillator.

' Y CHARLES H. SHAW.:

REFERENCES CITED The following references are of record in' the le of this patent:

' UNITED s'rA'rEs PATENTS Alexanderson Dec. 3, 194:6y 

